The Research And Modification Of Ba₂Ti₉O₂0 High Frequency Ceramic System With Meduium Permitivity

The microwave properties of Ba₂Ti₉O₂₀ (call B₂T₉ for short) was discussed in thispaper. It was difficult to prepare the single phase B₂T₉ by solid state reaction , sincethere are various thermodynamically stable compounds in the vicinity of the desiredcomposition of TiO₂-rich BaO-TiO₂ system. Furthermore studies revealed that thetemperature for a stable B₂T₉ was high and when it was higher than 1420℃the phaseunderwent a decomposition. Low melting glass additions, chemical processing andstarting materials with smaller particle sizes are employed to reduce the sinteringtemperature of B₂T₉ in this paper.The B₂T₉ synthesized with smaller particle sizes were more dense, and the grainwas granular with uniform size. The results showed that the sintering temperature wasdecreased and the best dielectric properties were obtained when sintered at 1240℃:tanδ=1.4×10^-4。From the result of XRD, we can see that with the increase of BaB₂O₄,the amount of B₂T₉ phase decreased greatly and BaTi₄O₉ phase became the majorphase, and a new phase BaTi(BO₃)₂ was synthesized, thus explained why thedielectric constant of B₂T₉ decreased with the increase of BaB₂O₄. The results showedthat the samples doped with 2wt% of BaB₂O₄ sintered at 1240℃have the lowestdielectric loss : tanδ=1.03×10^-4. The result of samples synthesized through sel-gelshowed that when calcined at 700℃, 750℃and 800℃, the main phase wasBaTi₅O₁₁,BaTi₄O₉ and B₂T₉ respectively. When doped with H₃BO₄, the dielectricconstant of the sample obtained by sol-gel method increased with the H₃BO₄ whilethe dielectric loss decreased ,and the sample could be well sintered at 1240℃.